Method and means for automatically regulating the resistance of a magneto safety gap



May 6, 1924.

D. GREGG METHOD AND MEANS FOR AUTOMATICALLY REGULATING THE RESISTANCE OF A MAGNETO SAFETY GAP Filed 001'.. 7. 1922 Patented May 6, 1924.

UNITED STATES DAVID GREGG, OF DAYTON 01H10.

METHOD AND MEANS FOR AUTOMATICALLY REGULATING MAGNETOA SAFETY GAP.

RESISTANCE or A Application filed October 7, 1922. 'Serial No. 593,133.

To all whom c't may concern.'

Be it known that I, DAVID GREGG, a citizen of the United States, residing at Da ton, in the county of Montgomery and tate of Ohio, have invented certain new and useful Improvements in Methods and Means for Automatically Regulating the Resistance of a Magneto Safety Gap, of which the fol1owing1 is a specification.

his invention relates to the automatic regulation of spark gaps or more particularly to the regulation of the resistance across a safety spark gap for airplane engine magnetos, in particular those magnetos used on overcompressed or supercharged engines.

It is well known that the dialectric strength of air decreases on rarefaction. The atmosphere above the earths surface decreases in density as the altitude above the earths surface is increased. Thus it is clear that as an airplane ascends, the dialectric strength of the air between the contact points of a safety s ark gap of a magneto thereon decreases. n a standard airplane engine the compression pressure in the cylinder also decreases as the airplane ascends, as this pressure is equal to thev compression ratio of the engine times the atmospheric pressure at whatever altitude the engine is. (This is neglecting the increment of pressure due to the heating of the incoming charge, and to the residual heat in the cylinder.) Thus there is practically a constant ratio between the atmospheric pressure at the safety spark gap, and at the points of the spark plugs, and as the resistance of the safety spark gap is initially set higherthan the resistance at the spark plugs the spark will always jump at the plugs as their resistance will always be less than at the safety gap.

O11 an overcompressed or supercharged engine the conditions are altered, as the compression pressure will be practically constant at any altitude at which the airplane may be flying. This is because the engine is always supplied (by means of the supercharger or ot er device) with intake air at a constant pressure., Hence it is clear that as a supercharged engine ascends the resistance at the plugs remains constant (as the pressure is constant) while the resistance across the safety ga decreases (as the atmospheric -pressure ecreases), and a point will be reached where the voltage will break down the safety gap, and a spark will jump there.

tional to the pressure and the potential difference required to produce a spark between rounded metallic surfaces varies almost as the distance between them and as the ressure in The Principles of Electric ave Telegraphy and Telephony-J. A. Fleming.

Heretofore no one to my knowledge has devised any means for accomplishing the purposes hereinafter described although in the use of the ordinary ,stationary spark gap man accidents have been caused. It is practical y impossible to use magnetos for high altitude work yif they have been constructed for low altitude work or should the spark gap of the magneto be adjusted for high altitude work the magneto will have substantially no regulation for low altitude work.

With the above and other facts in mind one object of my invention is to provide a means whereby to automaticallycontrol the resistance across the. safety gap regardless of the surrounding atmospheric pressure and at all times. It is a further object of my invention to provide simple and expedient means for accomplishing this automatic control, which will be responsive in direct proportion or in any desired ratio to the pressure of the surrounding atmosphere at any altitude at which an aircra t upon which the magneto may be mounted is iying.

Other objects will become apparent as the description of my invention proceeds from the claims and from the drawin in which:

Fig. 1 is a plan view of an em odiment of my invention.

Fig. 2 is a side sectional elevation thereof and;

Figs. 3 and 4 are graphic illustrations of gap variation with altitude and resistancel variation with altitude, respectively.

As illustrated in Figsa 1 and 2 my invention as at resent embodied consists a base 2 of suita le insulating material upon which v is mounted an upright fulcrum member v4 securedthereto as by'screws 6. Between the support 22 secured at 24, 26 to th insulatlng base2. A second bracket 28 is secured to the base 2 and has mounted thereon anadjustable contact 30 which is in turn connected through wire 32 to a binding post 34 secured in the base 2. A similar binding post 38 secured to the base in a similar manv ner as binding post 34, connected through wire 38 to a contact member 40 mounted in cooperative relation to the contact 30 on the end ofv lever 14. The binding posts 34, 36 serve to' connect the spark gap 1n the magneto circuit in the same manner as heretofore employed. An suitable damping means for damping out vibrations or oscillations of the lever 14 may be utilized.

The bellows 20 is composed. of thin metal and may be arranged in any'position with respect to the fulcrum pivot 12. It may contain a gas at a pressure above atmos heric pressure, or the gas may be at or un er atmospheric pressure. Corresponding corrections and detailing of thel mechanism will be made in all such cases however. l

'Ihe operation of the-device shown will be obvious. As the aircraft ascends, the ressure surrounding the diaphragm or be l ows decreases allowing the bellows to expand, moving the lever 14 down and widening the gap, t us keeping the resistance across the variable gap constant.

Fig. 3 is a graph with any gapopening (in the case shown the gap width is taken as unity at sea level), of my variable spark gap, showing how the gap opening increases with an increase of altitude. Fig. 4 is a graph illustrating (with legend) the variation in resistance across the stationary spark gap and how I secure constant resistance by compensating for such variation in resistance across my variable spark gap through wide pressure ranges. It will be noted that there is practically no variation in resistance across the variable gap under increasing or decreasing atmospheric pressures,

anse

l nThe objects accom lished by variable gap may'be-'accomp lshed by enc osing the ga or the magneto and gap within an airl tig t closure and maintalnmg atmospheric pressure at sea level therein.j

I claim: I 1. A spark gap com rismg spaced contacts and means adapte to maintain a constant resistancel thereacross upon variation Vof a resistance factor in the medium between said spaced contacts.

2. A pair of spaced contacts and means Aadapted to automatically maintain a constant resistance'thereacross upon variation of a resistance factor in the medium said spaced contacts. v

3. A pair vof spaced electrical contacts adapted to be subjected to and dependent upon a medium having variable resistance characteristics and means responsiveto said characteristics to maintaina constant resistance across said contacts.

4. In a safety spark'ga forv aircraft magbetween netos, contacts separated y a gap, means responsive to variations in atmospheric condit-lons to vary said ga 5. In a spark gap or an electric distribution system for aircraft, contacts separated by a gap, means directly responsive to a variation in atmospheric pressure to vary said gap. tion system for aircraft, means directly re- -sponsive toatmospheric temperature and means cooperative with said rst mentioned means to vary said gap.

7. In a spark gap for an electric distribution system for aircraft, contacts separated by a gap, means proportionately and automatically responsive to atmospheric pressure variations to maintain constant resistance across said gap.

8. In a device of the character described, a pair of contacts spaced by a spark gap, and

means 'responsive in direct proportion to anv atmospheric characteristic to vary the rela- Itive dlstance of said contacts.

9. In a device of the character described, a vlixed contact, a movable contact, and a pressure-responsive element adapted to vary effective distance between said fixed contact and said movable contact.

In testimony whereof I aiix my signature.

` i DAVID GREGG.

In a spark gap for an electric distribu- 

